For the size of the vehicle the MPG still seems respectable but I'm more cncerned with the emissions output. Do they have numbers for it yet? Oops, say the link, going to check it out.

I agree with you Evan.

I looked up the pollution score on FuelEconomy.gov and it didn't list the "EPA Air Pllution" score. Grrrrr It did list the carbon footprint score of 6.2 annual tons emitted compared to the Prius at 4.0. I'll see if I can find it somewhere else.

I wonder how these TDI engines go for diesel particulate exhaust.... a lot of advertisements will tout how low the diesel's CO2 emissions are, but don't mention other things like HC's, NOx and diesel particulate exhaust.

I'm always a bit surprised when I drive behind even relatively new diesel cars and see how much black soot covers the rear bumper close to the exhaust pipe -- imagine how much more particulates are clogging up the atmosphere!

I think this is a huge dissappointment for TDI fans. When I bought my prius, all kinds of fanboys gave me alot of noise on how the Diesel was going to bury the Prius in fuel efficiency. Although the numbers are respectable, they are not better then the prius.

And "clogging" up my lungs. They friggin stink!!!

I wash my roomate's 2006 GMC Duramax diesel for him and I always have to scrub the fender near the tailpipe because of the nasty soot that accumulates.

Octane means eight carbon molecules. Gasoline consists of molecules that are mostly close to eight carbons. Diesel consists of molecules that are mostly around 18 carbons. If you put diesel into a hydrocracker, with conditions adjusted to produce two nonane (nine carbon) molecules from every 18-carbon diesel molecule, you would effectively create two gallons of gasoline for every gallon of diesel that you began with. (I have a B.S. in biochemistry). If a given gasoline car gets 24mpg, then the diesel analogue (same vehicle, same engine displacement) usually gets around 48mpg. (Look at the figures for yourself).

The automakers advertise that diesel gets double the mileage of a gasoline car, but they don't tell you what I just told you. Diesel is NOT more efficient than gasoline, it is just a more dense fuel. More energy can be stored per liter than gasoline. Is wood heavier than cardboard of the same size? Does wood burn longer than cardboard of the same size? Yes and yes. Same concept with diesel versus gasoline. The material is more dense; there is more energy per unit volume.

This is why semi-trucks use diesel. For every 100 gallons that they have in their tanks, it would take 200 gallons of gasoline to do the same. This would not be feasible to carry around, everywhere they go.

Sorry Rybold, but that is totally wrong. You would have twice the number of moles, but as each molecule has half the mass, so you would end up with more or less the same volume, actually about 1.1 gallons since octane has a slightly lower gravimetric density than diesel.

In terms of energy content, it is true that diesel contains on average 12 - 15% more energy per gallon than gasoline. However, the great fuel economy of diesel vehicles comes mainly from the better thermal efficiency of the compression ignition diesel engine (at 40 - 45% efficiency) compared with gasoline spark ignition engines (at 25-30% for normal otto cycle).

Toyota realised that this is the big problem with using gasoline, so had to switch from Otto-cycle to an 'Atkinson'-like cycle in their Prius to allow a more diesel-engine-like 13:1 expansion ratio. This enables a peak thermal efficiency of 36%, and is the key reason for the Priuses improved economy.

However, the Prius engineers realised that such an engine would be almost undriveable (lack of low end torque and ramping issues etc), so had to resort to some kind of assist feature. This is why they eventually adopted a hybrid electric approach. Many people think that the hybrid-electric component of the Prius was designed to allow regenerative braking - it was NOT, and this only contributes about 2% to the improved economy of the Prius. The hybrid electric system was deployed so that Toyota could use a 13:1 expansion ratio engine with high efficiency (ie 36%).

I will join from a cost-efectiveness perspective....

2008 Prius Combined Rating:..........48 mpg

2009 Jetta TDI Combined Rating:.....34 mpg (m/t score)

12,000 miles/year

Fuel Costs (current)
Regular Unleaded:......................$4.05/gallon (S.F. Bay Area)
No. 2 Diesel:.............................$4.50/gallon (Read it and weep)

Annual Fuel Cost ([(miles/year)/(Combined Rating)] x Fuel Cost)
2008 Prius:................................$1,012
2009 Jetta TDI:...........................$1,588

Even with the dollar not buying much these days, $500 is half again what is takes to fuel the Prius.

Oh BTW, gas prices aren't staying constant in my neck of the woods, so expect the cost of gas & diesel to continue to increase.

My prediction: VW won't sell that many Jetta TDIs.
My second prediction: Toyota will continue to sell as many Prius as it can produce.

Another advantage of diesel engines is the lack of a throttle. This greatly cuts pumping losses during low speed operation. Toyota's hybrid system allows the gasoline engine to shut down at low speeds, which bypasses this loss altogether at low speed.

Tom

I own both the Smart Fortwo and a 2007 Prius. Actual mileage on my Smart and others is 38 in the city. Also you left out the comparison of cost. VW is way more expensive than a Smart.

There is much wailing and gnashing of teeth over at TDIclub.com! The great debate for the last year has been how VW was going to increase horsepower from 100 to 140, add emissions equipment, and increase highway FE to 60 mpg.

My experience says that the new 2.0 TDI will easily beat the 2008 EPA numbers. I have found that the old EPA numbers were very accurate for my 2003 TDI. If you go by those numbers the 2.0 TDI will get 36/39/45 mpg. (BTW, the EPA knows that the official EPA numbers are low for diesels by about 18%)

From page 8: http://www.epa.gov/fueleconomy/420r06017.pdf

"As can be seen, diesels appear to perform the best with respect to their label fuel economy, outperforming the label by 4.3%. Conventional gasoline vehicles come very close to meeting their label, falling short by only 1.4%. Conventional vehicles with relatively high combined fuel economy (here assumed to be 32 mpg or more, representing the top 10% of conventional vehicles in terms of fuel economy) performed only slightly worse, falling short by 1.7%. Hybrids fall short by a much larger margin, 8.2%. Thus, the greater shortfall seen with hybrids appears to be more related to hybrid technology than to simply high levels of fuel economy.

With respect to the mpg-based label values, diesels still perform the best of the four types of vehicles, now exceeding their label values by 18%.b Those conventional vehicles with relatively high fuel economy fall next, followed by the typical conventional vehicle and hybrids. Thus, the YourMPG estimates indicate that hybrid performance differs from that of conventional vehicles, including those with high fuel economy."

(NOTE: "Label Fuel Economy" is old EPA numbers used up until 2008)

The EPA numbers will make the TDI's a harder sell now that diesel is ~ 19% higher than regular gasoline. However, VW can still sell these cars if they use the right presentation. They need to move people away from the $/gal to $/mile. If you look at $/mile the following happens:

Vehicle --------------HP----lb-ft------Mileage -------Fuel ---------$/gal ---------$/mile
2.5 VW Jetta --------170----177-----21/24/29 -----Regular -------$3.79 ---------$0.172
2.0T VW Jetta-------200----204-----22/25/29 -----Premium -------$3.94 ---------$0.164
2.0TDI VW Jetta-----140----235-----30/34/41 ------Diesel --------$4.49 ---------$0.132

The TDI has the most expensive fuel but the lowest cost per mile.

I don't know how VW will sells 2.5L Jettas. It will now most likely be slower and more importantly feel much slower than the TDI and get 30% lower fuel mileage. US Pricing has not been announce but in Canada the TDI is only $1400 (5%) more than the the 2.5L.

Evan

I had quite a long discussion over at the FJ forum about why diesel is a dead end. Even the latest EuroIV and upcoming EuroV diesel emissions specs will allow 5-7 times the PM10 and NOx as a gasoline engine

Remember the Europeans put a lot more emphasis on CO2 or the "greenhouse gas." Our EPA, and especially states with California Emissions, put a lot more emphasis on health and safety, thus they heavily regulate smog and carcinogenic output like PM10 and NOx.

One thing *not* regulated is dioxin. Diesel exhaust contains dioxin, not too many folks know that

Once you tack on all the emissions stuff to a diesel engine, the relative fuel economy difference begins to go away. Diesel fuel in most European countries isn't as heavily taxed so it's still cheaper to drive a diesel in the EU

Even with the emissions stuff tacked on, it's easy to find fairly new VW TDI cars with the black soot residue around the exhaust area. No thanks

http://www.toronto.ca/health/pdf/de_technical_appendix.pdf

http://www.ucsusa.org/assets/documents/clean_vehicles/dieseldilemma_fullreport.pdf

Sick of Soot: Solutions to California's Diesel Pollution

Now, diesel proponents will scream about this. Hell, a lot of them claim the black exhaust pouring out is "harmless" so I'm unsure of what sort of fantasy la-la land they live in

jay

Our boat diesel has a built-in system for keeping black soot out of the atmosphere: it collects it on the transom and back half of the boat. Black soot is an ongoing battle for us - it sticks to white paint like glue.

Tom

In a modern petrochemical environment, there are many ways to stretch the yield beyond "straight run" petrol and distillate. I'll touch on a few of these, if you wish I can dramatically expound on it

After simple distillation in a crude distillation unit, one can apply vacuum distillation to send process to send the volatiles to naphtha hydrotreating. The volatiles from the first stage CDU simple distillation is also sent to naphtha hydrotreating – at one time these were flared off

The CDU makes use of multiple stages or trays that utilize pumparounds, or “reflux,†to continually cool and further flash the desired product streams

After naphtha hydrotreating, isomerization is applied which results in more petrol yield. The process stream is then sent to catalytic reforming to yield hydrogen, petrol, and aromatics

From around the mid column vacuum distillation the process stream is sent to a fluidized catalytic cracker, and to a hydrocracker. The hydrocracker receives residues from the FCC, which results in diesel, jet fuel, and other distillates

The FCC will produce cycle oil – low cycle oil and high cycle oil further on – to aid in hydrotreating and hydrocracking. The FCC will also produce petrol, and when the aromatics are sent through alkylation, more petrol

The residues from the FCC and vacuum distillation will be sent to a coker unit, which produces tars, asphalts, and petroleum coke

I’ve kept this very crude – pardon the pun – and simple. For example, I’ve ignored desalting. I’ve also ignored the different yields from different crude sources, Light Brent Sweet is the best for petrol and lighter distillates, Venezuelan is about the worst.

I’ve also ignored the massive potable process water consumption of the petrochemical process. As an example, a typical 250,000 BPD (Barrel Per Day) refinery will consume around 10,500,000 US gallons of crude, as one barrel is precisely 42 US gallons. That same refinery will also consume around 10 million US gallons of process water

WHich is why I get all excited when you, Tom, or Hobbit "talk dirty" like that

Your example would be applicable if the buyer was only looking at VWs. I am not aware of many car buyers that limit their selection to just one manufacturer. While it may be technically correct that the TDI has the lowest cost/mile of the VWs, each time someone fills up the TDI and has to pay $4.50+/gallon and they see a Prius filling up for ~$0.50/gallon less and then they remember that the Prius gets better economy, they will be hating the decision to get the TDI. In the S.F. Bay Area, Prius' are basically pre-sold. If you go to a dealer and want to buy a Prius, you are told you will have to wait for one to arrive. Depending on how many have been pre-sold, you could be looking at a 1-2 month wait for the car. It is getting back to where things were at in 2004 & 2005 where there was a 90 - 120 day wait for the cars and dealers were selling at MSRP.

your diesel price is too low

Per http://www.fuelgaugereport.com/CAmetro.asp, the avg. price of regular in SF is $4.066/gal. The avg. price of diesel is $4.938/gal.

Re: your diesel price is too low

My error (on the Diesel No. 2 price). The last time I checked Diesel prices was a few weeks ago. At an $0.87/gallon differential, the negative benefit (of Diesel) gets even worse.

I stand by my predictions, however.